1. Field
The present disclosure relates a thermoelectric material, a thermoelectric element and a thermoelectric module including the same, and a method of preparing the thermoelectric material.
2. Description of the Related Art
A thermoelectric phenomenon is a reversible, direct energy conversion from heat to electricity and vice versa, which occurs when electrons and holes move within a material.
One example of the thermoelectric phenomenon includes the Peltier effect, in which two dissimilar materials are connected at a contact point where heat is released or absorbed due to a current applied from the outside. Another example is the Seebeck effect, in which an electromotive force is generated due to a temperature difference between the ends of the dissimilar materials that are connected at the contact point. Another example is the Thomson effect, in which heat is released or absorbed when a current is applied to the material having a predetermined temperature gradient.
When thermoelectric materials are used, low-temperature waste heat may be directly converted to electricity, or heat generated from electricity, thus energy use efficiency may be increased. Also, thermoelectric materials may be applied in various fields to provide devices such as a thermoelectric generator, a thermoelectric cooler, or the like.
The performance of a thermoelectric material is evaluated using a dimensionless figure of merit ZT defined by Equation 1:
                    ZT        =                                            S              2                        ⁢            σ            ⁢                                                  ⁢            T                    κ                                    Equation        ⁢                                  ⁢        1            
In Equation 1, ZT is a figure of merit, S is a Seebeck coefficient, σ is an electrical conductivity, T is an absolute temperature, and κ is a thermal conductivity.
To increase energy conversion efficiency, a thermoelectric material having a high Seebeck coefficient, a high electrical conductivity, and a low thermal conductivity is desired, but generally, a Seebeck coefficient, an electrical conductivity, and a thermal conductivity have a trade-off relationship.
Because a nanostructure has a small particle size compare to a bulk material, an intragranular density can increase, and thus scattering of phonons at interfaces of the nanostructure can increases. In this regard, thermal conductivity can be decreased, and the trade-off relationship between a Seebeck coefficient and an electric conductivity can collapses due to a quantum confinement effect, and a figure of merit may increase.
A nanostructure may be, for example, a superlattice thin film, nanowires, quantum dots, or the like, but manufacture of such nanostructures is difficult, and a figure of merit in a bulk material is low.
Therefore, a nanostructure that provides a simple manufacturing process and an improved figure of merit in a bulk would be desirable.